If the science-fiction makes us dream, it may also give nightmares, in a chaotic and dystopic aspect, like in the Matrix saga that shows us an universe controlled by machines, and where the humans are slave of their system, running their development .
The Black Mirror serie is also a specialist in this kind of stories : worlds where the humanity loses it’s place in nature, or is enslaved by a powerful and more evolved population.
These stories may confuse and scare most of people, because we lose the feeling of safety and control that we have knwon for so long, these fictional worlds are so far from our lives, and scare by a huge difference in tehcnologies, the place of the human in the society : maybe we will lose control of our technology, and the society could not stop a bad evolution, in the worst scenario.
Another fear of the human on a future aspect is the isolation, knowing that we are alone in this universe, or cut from the world, may make a man crazy, thinking that there is nothing outside of our planet is a thought that go against the principle of the research, if there is nothing to search, there is no more reason to answer questions of the universe.
This fear is very well illustrated in the Neon Genesis Evangelion serie, because all of the cast have to accept the idea of battling divine creatures, without knowing what they are, what they want or why they want to destroy the world. They must fight things that is out of our minds, knowing one thing : the future of humanity is on their shoulders, they can not fail their missions. All of these informations put them in existential questions and philosophical choices.
At the end, science-fiction shows us some terrifying concepts : the lose of controls over the technology, to a replacement of this one on the humanity, that could be a threat to the most important thing it possess, its freedom. Some works have very well understood this idea, like the movie 2001, space odyssey, or 1984 from Georges Orwell, in these cases, the creepy idea of a dystopic future seems possible, even in a irational way.